Describe the forces acting on an object on earth falling through the air, and how they change from when the object is first released into the air leading to terminal velocity.

The two forces acting on the object are weight due to gravity pulling the object towards earth, and drag resisting this motion. When the object is first released, drag is small as velocity is low, so the resultant force is down. This means the object accelerates towards earth. As the object gains speed, drag increases until it equals the magnitude of the force down due to gravity. At this point, resultant force is zero and so the object stops accelerating, and maintains the same velocity. This is called terminal velocity.